Over the past several decades, continuous strides have been made to improve the treatment of diabetes mellitus. Approximately 90% of people with diabetes have type 2 diabetes, also known as non-insulin dependent diabetes mellitus (NIDDM). Type 2 diabetics generally still make insulin, but the insulin cannot be used effectively by the body's cells. This is primarily because the amount of insulin produced in response to rising blood sugar levels is not sufficient to allow cells to efficiently take up glucose and thus, reduce blood sugar levels.
A large body of pre-clinical and clinical research data suggests that glucagon-like peptide-1 (GLP-1) compounds show great promise as a treatment for type 2 diabetes and other conditions. GLP-1 induces numerous biological effects such as stimulating insulin secretion, inhibiting glucagon secretion, inhibiting gastric emptying, enhancing glucose utilization, and inducing weight loss. Further, pre-clinical studies suggest that GLP-1 may also act to prevent the B cell deterioration that occurs as the disease progresses. Perhaps the most salient characteristic of GLP-1 is its ability to stimulate insulin secretion without the associated risk of hypoglycemia that is seen when using insulin therapy or some types of oral therapies that act by increasing insulin expression.
However, development of a GLP-1 therapeutic has been extremely difficult. This is primarily due to the instability of the peptide during manufacturing processes, in solution formulations, and in vivo. The only published clinical studies employing GLP-1 compounds to treat hyperglycemia or other conditions involve formulating GLP-1 compounds such that they can be delivered by subcutaneous injection or through continuous subcutaneous infusion or continuous intravenous administration. Many type 2 diabetics or obese patients desiring to lose weight will not be willing to undertake a treatment regimen that may involve several injections per day. Thus, there is a need to develop GLP-1 compound therapeutics that can be delivered by an alternative non-invasive means such as by oral delivery.
Unfortunately, there are numerous barriers to effective oral delivery of peptides. The high acid content and ubiquitous digestive enzymes of the digestive tract will often degrade proteins and peptides before they reach the site of absorption. Further, many peptides cannot effectively traverse the cells of the epithelial membrane in the small intestine to reach the bloodstream. Finally, many drugs become insoluble at the low pH levels encountered in the digestive tract and, thus, are not absorbed effectively.
The fact that GLP-1 compounds are relatively unstable in solution formulations, only remain in solution under a fairly narrow set of conditions, and have a relatively short in vivo half-life when administered as a solution formulation, suggested that these compounds could not be effectively delivered through the oral route. Thus, it was surprising that GLP-1 compounds could be formulated such that biologically active molecules were absorbed into the blood stream after oral administration.
The present invention involves the use of specific delivery agent molecules that interact with GLP-1 compounds in a non-covalent fashion to allow the compounds to cross gut membranes and yet remain therapeutically active. Although the delivery agents employed in the present invention have been disclosed in a series of U.S. patents (see U.S. Pat. Nos. 5,541,155; 5,693,338; 5,976,569; 5,643,957; 5,955,503; 6,100,298; 5,650,386; 5,866,536; 5,965,121; 5,989,539; 6,001,347; 6,071,510; 5,820,881; and 6,242,495; see also WO 02/02509; WO 01/51454; WO 01/44199; WO 01/32130; WO 00/59863; WO 00/50386; WO 00/47188; and WO 00/40203), oral administration of formulations comprising GLP-1 compounds with these delivery agents has not been disclosed or suggested. Further, numerous parameters impact whether a particular class of compounds can be effectively delivered in combination with one or more classes of delivery agents. For example, the conformation of the peptide, the surface charges on the molecule under certain formulation conditions, the solubility profile, the stability as a formulated component, as well as susceptibility to protease digestion and in vivo stability all influence the ability to deliver a compound orally.